In (1) and (2), Descartes appeals to his concepts of mind and body. Earlier in the Meditations, he analysed mind as something that thinks and body as something that is extended (has a size and takes up space). We can understand (1) and (2) to entail the claim that it is conceivable that mind can exist without body. Nothing in our concepts rules this out.
In Meditation VI, Descartes adds (3). Assuming that God is omnipotent, the only reason for thinking that God cannot make something is that the concept of it is contradictory. The concepts of mind and body aren't self-contradictory. So God can create the mind and the body just as Descartes conceives of them - a thinking thing and an extended thing. We can summarize (3), (4) and (5) in terms that don't refer to God: it is possible that mind can exist without body. Finally, a quick reminder helps in understanding the inference from (5) to (6). A substance, we said above, is something that does not depend on another thing in order to exist. In other words, a substance can exist independently, on its own.
If the mind and body are two distinct things, how are they related? Descartes says that Nature also teaches me, through these sensations of pain, hunger, thirst and so on, that I (a thinking thing) am not merely in my body as a sailor is in a ship. Rather, I am closely joined to it - intermingled with it, so to speak - so that it and I form a unit. (p. 30) Because 'a unit' doesn't sound like 'two separate things', this claim and its implications are puzzling.
Reflecting on perception, sensation and feeling, we notice that we perceive that we have bodies, and that our bodies - this particular physical object that we have a close and unique relationship with - can be affected in many beneficial and harmful ways. This is brought to our attention through our bodily appetites, like hunger and thirst, through emotions, such as anger, sadness, love, and through sensations, like pain, pleasure, colours, sound and so on. All these experiences have their origins in the body.
Given that the union of mind and body is a third 'basic notion', is it a notion of a third type of substance? Is there one new type of thing here, created from the unification of two distinct types of thing? Descartes says, in a letter to Regius, December 1641, that 'since the body has all the dispositions necessary to receive the soul, and without which it is not strictly a human body, it could not come
about without a miracle, that a soul should not be joined to it'. The comment that, unless united to a soul, a body is not a human body, suggests (but not conclusively) that the 'human body', body and soul together, can be considered as a substance in its own right, a substance created from the union of body and soul.
However, philosophers don't agree on whether or not this is the implication we should draw from his union theory.
To the question, 'What am I?', Descartes' first answer is 'a thing that thinks', and he repeats in Meditation VI that we can imagine ourselves existing 'whole' without feeling or imagination. But is it any less true to say 'I am a human being, a union of mind and body, an embodied mind' than 'I am a mind'? The mind takes on the body's experiences as its own, i.e. we refer our sensations, emotions, etc., to our selves. We 'own' these states just as much as we 'own' our thoughts. We experience ourselves as embodied minds, not just minds. Descartes accepts all this, but his argument that minds can exist without bodies leads him to say that to lose the experiences that depend on the body would not
be to lose our identities